Copper-containing catalysts are used in industrial processes to a considerable extent; for example, they play an important part in hydrogenation and dehydrogenation processes. In this instance, the feedstock is passed to the fixed catalyst either in the gaseous state (gas-phase operational mode) or in the liquid state (liquid-phase operational mode). The catalyst can also be used in a finely dispersed state as a suspension (suspension operational mode).
Very wide use has been made of catalysts which, in addition to copper, also contain chromium, inter alia for the hydrogenation of esters. These catalysts are known as copper chromite catalysts or Adkins catalysts.
However, the use of Adkins catalysts is not without problems, because their preparation makes use of chromium (VI) compounds which are considered to be carcinogenic and thus, in handling them, appropriate protective measures are required. Furthermore, in the course of their preparation, relatively large quantities of waste waters are produced which are heavily polluted with compounds of copper, chromium (VI), and ammonium salts. Waste waters of this type are undesirable because compounds of both copper and chromium (VI) are highly toxic to micro-organisms and must be removed from the waste water by laborious--and hence expensive--treatment.
Occasional use is also made of copper catalysts containing no chemically bound chromium for the hydrogenation of esters. According to U.S. Pat. No. 4,199,479, supported catalysts containing copper, zinc oxide and, if required, cobalt are suitable for this purpose. EP-B 74,193 describes a process for the hydrogenation of esters in the gas phase by means of a catalyst containing copper and zinc oxide. Chromium-free copper catalysts are also often recommended for other reactions.
Thus, DE-OS 20 56 612 describes a catalyst comprising mixed crystals from the series (Cu.sub.x Zn.sub.y)Al.sub.2 (OH).sub.16 CO.sub.3.4H.sub.2 O, where x and y can assume numerical values of 0.5 to 5.5 and x plus y equals 6. The mixed crystals are obtained by precipitation at a pH between 4.5 and 5.5, by adding a basic precipitant (for example an aqueous Na.sub.2 CO.sub.3 solution) to an aqueous solution containing nitrates of copper, zinc and aluminum. The catalyst, which in the non-reduced form contains CuO, ZnO, and Al.sub.2 O.sub.3, is used in the conversion to methanol of a gas mixture comprising carbon monoxide, carbon dioxide, and hydrogen.
EP 125,689 relates to a catalyst containing CuO, ZnO and Al.sub.2 O.sub.3, having an atomic ratio Cu:Zn between 2.8 and 3.8 (corresponding to 26.9 to 36.5 parts by weight of ZnO per 100 parts by weight of CuO), and an Al.sub.2 O.sub.3 fraction from 8% to 12% by weight. Al.sub.2 O.sub.3 is used in the preparation as colloidal aluminum hydroxide; Cu and Zn are incorporated in the catalyst by precipitation from metal salt solutions. The catalyst is used for the production of methanol.
It is an object of the present invention to provide a process which makes it possible, not only to produce alcohols by catalytic hydrogenation of esters and fatty acids, but also to produce amines by catalytic hydrogenation of nitriles, with the use of a chromium-free copper catalyst. Furthermore, the process should ensure that the reaction, in particular at elevated temperatures, proceeds with high yield, high selectivity, and substantially avoids the formation of by-products. Also, the results achievable with conventional Adkins catalysts should not only be equalled but, in many cases, distinctly improved. A further advantage is found in the fact that the preparation of the chromium-free copper catalyst circumvents problems which are significant in the preparation of Adkins catalysts; e.g. the handling of carcinogenic chromium (VI) compounds, the production of waste waters containing noxious compounds, and the safe disposal of chromium-containing used catalysts.